An object of the invention is therefore to provide a burner for particulate materials which burner can be used in a variety of situations to burn, for example, wood waste, bark, wood chips, sawdust and other similar combustible particulate materials.
A number of constructions of burner for particulate fuels have been proposed in the past and these include fluidised bed burners and cyclone burners.
Fluidised bed burners are constructed with an active bed of material into which fuel is fed to incinerate the material. The problem with such burners is that if complete combustion does not occur the unburnt or partly burnt combustion products tend to clog up the fluidised bed. The bed itself must be of special materials and this results in added costs. Fluidised bed burners often require additional fuel to be added to sustain combustion and this again adds to running costs. The size of existing fluidised bed burners is such that they do not lend themselves to installation in some situations and they are normally better suited for the destruction of waste or to supply additional heat from waste products at large scale industrial sites.
A number of constructions of cyclone burner for a range of particulate fuels have been proposed. Examples include the burners described in U.S. Pat. Nos. 4,597,342, 4,574,711, 4,561,364, 4,572,084 and 2,707,444 and European Pat. Specification No. 0 006 974.
In the said European Specification No. 0 006 974 is described the cooling of a complex burner by providing a spirally wound space around the burner shell. The burner being of the type constructed with a ceramic cladding. Although such a burner may be able to withstand the temperatures produced by normally combusting fuel in the chamber such a burner cannot withstand the temperatures produced during combustion with the present invention. The applicants experiments with refractory linings and ordinary steel as a firebox have shown that the linings deteriorate rapidly under the heat produced and that an ordinary steel firebox distorts in shape if high temperatures are produced in the burner.
Similar problems exist with the burners described in U.S. Pat. Nos. 2,707,444 and 4,574,711.
The constructions of burner described in Green et al's U.S. Pat. Nos. 4,597,342, 4,572,084 and 4,561,364 are cooled by the inclusion of a heat exchanger for water on the outside of what is a pre-entry chamber. It is the applicant's experience that such cooling is only effective to a limited degree and in any event is directed to adapting an oil burner to operate with a mixture of coal dust and gas. Such a construction is in the applicants opinion very distinct from the present invention which is designed to operate with particulate wood, sawdust and the like. The problems inherent in burning of this material are very different from the problems of combusting coal dust and gas.